Add job code attachment Langfuse tags

[hanna-paasivirta]

Short Description

Adds a has_code_attachment tag to Langfuse that gets attached to a trace whenever the job code agent actually returns code changes (whether used directly or through global chat). This allows us to filter in Langfuse for AI generated code so we can run specific evaluators only on those traces.

Fixes #551

To test locally, you will need to generate the following Langfuse keys in a personal project in your .env in services/:

LANGFUSE_SECRET_KEY
LANGFUSE_PUBLIC_KEY
LANGFUSE_BASE_URL

AI Usage

Please disclose whether you've used AI in this work (it's cool, we just want to
know!):

• Yes, I have not used AI
• No, I have not used AI

You can read more details in our
Responsible AI Policy